Friday, April 08, 2005

Cassini Significant Events for 03/31/05 - 04/06/05

The Significant Events report for this week is out, though it doesn't seem to have shown up on the JPL website yet but it has gone out to certain mailing lists. The big event over the last week has been T4. This was the first encounter of Titan in which we were just on reaction wheels rather than thrusters (which require precious hydrazine) to control stability and pointing. Thrusters are usually needed when the spacecraft dips below 1100 km altitude (give or take 100 km) from Titan because of torques applied to the spacecraft by Titan's, which, while thin at that altitude, is still dynamically significant. Anyways, based on the telemetry acquired after the encounter, the reaction wheels appeared to work nominally and were sufficient for controlling the spacecraft with a flyby at 2400 km (I would hope so!!). Interesting that ISS was not mentioned in this part but other instruments were...

This release also confirms that the Tethys tweak, calling for a new targeted flyby of Tethys, has been officially approved. I guess it was only provisionally approved, or approved by a smaller working group last week. The Tethys tweak came out of a requirement to avoid the E-ring crossing on Rev15. A 1500-km Tethys targeted encounter shook out of this required change. IOW, the trajectory needed to be tweaked to avoid this crossing, and it only required a little extra delta V to produce this targeted flyby and a closer flyby of Hyperion a few days later (1000 to 500 km). Apparently, nearly a dozen science objectives from the Cassini AO will be accomplished by this tweak (not bad!).


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